Characteristics of neutrons

The characteristics of neutrons

Neutrons are electrically neutral but have a spin, or magnetic moment, so they they are sensitive to magnetic sources in condensed matter and can provide images of magnetic structure. Neutrons have the ability to deeply penetrate matter, they interact with nuclei and neutrons – unlike X-rays – can distinguish light elements such as hydrogen.

Below we present 5 characteristics of neutrons, and 5 good reasons to use them for research.

Click for an example.

Electrically neutral, they can go deep into matter

Neutrons are non-destructive and can penetrate deep into matter. This makes them an ideal probe for biological materials and samples under extreme conditions of pressure, temperature, magnetic field or within chemical reaction vessels.

Click for an example.

Microscopically magnetic, they can show magnetism

Because they possess a magnetic dipole moment, neutrons are sensitive to magnetic fields generated by unpaired electrons in materials, and they can be used to analyse the magnetic properties of materials, at the atomic scale. In addition, the scattering power of a neutron off an atomic nucleus depends on the orientation of the neutron and the spin of the atomic nuclei in a sample. This makes the neutron a powerful instrument for detecting the nuclear spin order.

Their Ångstrom wavelengths can show structure

Click for an example.

Neutron wavelengths range from 0.1 Å to 1000 Å, which is comparable to the distance of neighboring atoms in solid matter. This makes them an ideal probe of atomic and molecular structures, be they single atomic species or complex biopolymers. Like water waves at a barrier, neutrons are diffracted by the ordered atoms of a sample. The neutron diffraction angle is a sensitive measure for the distance of the atoms within the sample and therefore can give us information on the localisation of the atoms.

Click for an example.

Their energies of millielectronvolts can show motion

The energies of neutrons are of the same magnitude as the diffusive motion in solids and liquids, the coherent waves in single crystals (phonons and magnons), and the vibrational modes in molecules. It is easy to detect any exchange of energy between a sample of between 1microeV (even 1 neV with spin-echo) and 1eV and an incoming neutron.

Randomly sensitive, they can show hydrogen atoms

Click for an example.

With neutrons, the variation in scattering power from one nucleus to another within a sample varies in a quasi-random manner. This means that lighter atoms are visible despite the presence of heavier atoms, and neighbouring atoms may be distinguished from each other. In addition, contrast can be varied in certain samples using isotopic substitution (for example D for H, or one nickel isotope for another); specific structural features can thus be highlighted. The neutron is particularly sensitive to hydrogen atoms; it is therefore a powerful probe of hydrogen storage materials, organic molecular materials, and biomolecular samples or polymers.